Two natural disasters, the Great East Japan Earthquake in March 2011 and Heavy Rain in Niigata and Fukushima Prefectures in July of the same year, inflicted enormous damage on Tohoku Electric Power Company's electric facilities and disturbed power supply. Although some facilities have completely recovered from the damage, the rest in catastrophically affected areas is still in the midst of recovery efforts. This paper presents damage to facilities caused by the natural disasters and recovery situation.

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A method for determining line drop compensation (LDC) parameters and a control method for a step voltage regulator (SVR) using measurement data of a distribution system was proposed. Active and reactive power through the SVR and the voltage of each node of the distribution line were analyzed by multiple regression analysis to determine the optimum parameters of the LDC. The analysis results show that the SVR operated with the optimum parameters improves the voltage quality of the distribution line.

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This paper proposes a frequency control of a battery energy storage system applied for frequency deviation suppression in power system including a large amount of wind power generation. The power system of 5,000MW capacity with governor free control and load frequency control is assumed for the study, and wind power generation of 500MW capacity is assumed. The battery energy storage system is assumed to be added for the frequency control in the power system. Suitable frequency control functions of the battery energy storage system and suitable capacity of the battery energy storage system which coordinate with conventional frequency controllers in the power system are reported.

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Pulsed GTA welding has been used for improvement of stability, weld speed, and heat input control. However, the temperature and radiation power of the pulsed arc have not been elucidated. Furthermore, arc contamination by metal vapor changes the arc characteristics, e.g. by increasing radiation power. In this case, the metal vapor in pulsed GTA welding changes the distribution of temperature and radiation power as a function of time. This paper presents the relation between metal vapor and radiation power at different pulse frequencies. We calculate the Fe vapor distribution of the pulsed current. Results show that the Fe vapor is transported at fast arc velocity during the peak current period. During the base current period, the Fe vapor concentration is low and distribution is diffuse. The transition of Fe vapor distribution does not follow the pulsed current; the radiation power density distribution differs for high frequencies and low frequencies. In addition, the Fe vapor and radiation distribution are affected by the pulsed arc current frequency.

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This paper studies penetration depth and wave propagation in multi-layer ground. A relation between a wave propagation domain frequency, penetration dpeth and multi-layer ground parameters is estimated. An experimental setup is constructed to study the transient characteristics of spherical grounding electrode embedded into ground. The ground is analysed as homogenous ground, two-layer ground and multi-layer ground. To verify the proposed equations, a spherical grounding electrode is tested by injecting a step like current of different rise times into the spherical grounding electrode at different depths. The injected currents and voltages are measured and analysed. The electrode impedance shows dependence on the injected domain frequency and depth of the spherical grounding electrode at different ground layers. Numerical model is proposed by using the current source simulation method and the method of successive image technique. This model is used to investigate the penetration depth effects on grounding spherical electrode resistance in homogenous and two-layer ground. The experimental results verify the proposed estimated penetration depth equations.

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The corrosion behavior of aluminum wire used for overhead transmission line was studied in four corrosion environments: (1) sodium chloride solution, (2) sodium chloride solution with addition of alumina particles, (3) aluminum chloride solution, (4) aluminum chloride solution with addition of alumina particles. The corrosion test and polarization measurements reveal that the (2) and (4) environments with alumina particles roughened and rapidly corroded the surface of the aluminum wire. It is considered that the wet and dry environments of the overhead transmission line have changed aluminum hydroxide as corrosion products to alumina (aluminum oxide) which play polishing and gliding role to weaken the surface of the aluminum wire. It is also shown that the corrosion of the aluminum wire is categorized as an abrasive corrosion environment caused by alumina and corrosion fatigue by vibration of the wire in the sky.

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Effect of arc voltage on different factor of design and control was investigated for high current in order to develop design guide of circuit breaker. In this study, dependences on these factors which are current, arc length, surface area on electrode and internal pressure of arc voltage were evaluated quantitatively. As a result of the evaluations, it was estimated that arc voltage near electrode surface rise linearly with arc current and the area on the surface to the power -0.8, and the voltage in arc column rise pressure increase to the power 0.3. We confirmed the validity of the characteristics of the estimated voltage by comparison with the generated voltage in an actual arc extinguishing chamber. The characteristics of the estimated voltage would be provided as effective guidelines to design arc extinguishing chambers.

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A novel lightning risk assessment program has been developed. The program evaluates the lightning hazard level and lightning risk based on the lightning data, facility data and topographical data. Main functions of the program are as follows. 1) Lightning hazard maps can be shown on the meshes in Japan. 2) The program calculates lightning risk for transmission lines, distribution systems, wind turbines. The risk level at each area is shown in a form of a map. 3) The instantaneous voltage dip risk is evaluated from the data of lightning, locations of transmission lines and system configuration and the risk level at each node of a system is shown on the system map.

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